The present invention concerns the field of hybrid transmissions for motor vehicles comprising on the one hand a driving heat engine and on the other at least one electrical machine.
More precisely, the invention relates to a method for controlling recharging of the traction battery on a hybrid transmission for a motor vehicle equipped with a heat engine and at least one electrical machine, where the electrical machine is used as the sole motor-driven power source up to a speed threshold beyond which it is possible to couple the heat engine with the wheels, in hybrid modes, so as to run the power supplies from the heat engine and the electrical machine simultaneously with each other.
This invention can be applied in a non-limiting manner to a hybrid transmission for a motor vehicle equipped with a heat engine and a driving electrical machine, comprising two concentric primary shafts each bearing at least one reduction gear on a secondary shaft connected to the wheels of the vehicle and a first coupling means between two primary shafts, said coupling means being able to occupy three positions.
FIG. 1 describes a non-limiting example of a hybrid transmission having this principle of construction. This transmission comprises a solid primary shaft 1 connected directly by means of a filtration system (shock absorber means, “damper”, dual mass flywheel or other) 2 to the flywheel 3 of a heat engine (not shown). The solid shaft 1 carries an idler gear 4 able to be connected thereto by a first coupling system 5 (clutch, synchronizer, or other type of coupler, which may or may not be progressive). A hollow primary shaft 6 is connected to the rotor of an electrical machine 7, preferably (but not obligatorily) of the axial, disk-shaped machine type. Other types of electrical machine can also be used within the scope of the invention, for example radial machines, having an excitation magnet or coil, or reluctance machines. The hollow shaft 6 carries two fixed gears 8, 9. The hollow shaft 6 may be connected to the solid primary shaft 1 by means of the coupling system 5. A secondary shaft 10 carries two idler gears 11 and 12. The idler gears 11, 12 can be connected to the primary shaft by means of a second coupling system 13 (clutch, synchronizer, or other type of coupler, which may or may not be progressive). The secondary shaft 10 also carries a fixed gear 14 and a reduction gear 15 toward a differential 16 connected to the wheels (not shown) of the vehicle.
As indicated above, the first coupling means 5 may occupy at least three positions, in which:                the heat engine is decoupled from the kinematic chain connecting the electrical machine 7 to the wheels (position 1),        the heat engine drives the wheels with or without the contribution of the electrical machine (position 2), and        the heat engine and the electrical machine 7 are coupled so as to add together the respective torques thereof in the direction of the wheels (position 3).        
In the hypothesis in which, by construction, a vehicle equipped with such a transmission cannot use the heat engine to contribute to the pull of the vehicle below a speed threshold, the battery is primarily discharging at the low speeds of the vehicle. Beyond the speed threshold, the energy management system of the vehicle is capable of distributing the power between the heat engine and the electrical machine so as to ensure a minimum autonomy of the vehicle in electric mode. When the vehicle travels regularly below the speed threshold, there is the problem of providing an energy reserve in the battery in all circumstances so as to ensure at least the launching of the vehicle until the heat engine is started. Without this reserve of electrical energy, the vehicle is necessarily immobilized in a “roadside recharging mode”, in which the heat engine recharges the vehicle battery at standstill before the battery has sufficient energy to re-launch the vehicle.